Grinding machine and method for grinding a workpiece

ABSTRACT

Disclosed is a grinding machine comprising oscillating driving means ( 3, 4 ) for setting grinding means ( 1 ) into an oscillating grinding motion and an actuation device ( 7 ) that is provided with a plurality of actuation areas ( 8 ) which can be triggered such that different zones of the grinding means ( 1 ) are alternately actuated independently of the oscillating grinding motion.

FIELD OF THE INVENTION

The invention relates to a sanding machine having oscillation drivemeans for setting abrasives in an oscillating sanding movement.

Furthermore, the invention relates to a method of sanding a workpieceusing such a sanding machine by oscillating sanding movements.

BACKGROUND OF THE INVENTION

Such a sanding machine is described, for example, in the embodiment of abelt sanding machine in EP 0 543 947 B1. In this case, an abrasiveadhering to a plate is coupled by oscillation drive means to a sandingmachine frame in such a way that a translatory orbital movement issuperimposed on a second movement of the plate relative to the sandingmachine frame. The two superimposed movements are intended to prevent aregular sanding pattern from being produced. The two superimposedmovements are coupled to one another.

For example, EP 0 155 380 B1 discloses a belt sanding machine which hasa link pressure beam with a multiplicity of pressure shoes arranged nextto one another. The pressure shoes are triggered as a function of thecontour, to be processed, of the workpiece in such a way that only thepressure shoes actually required for the workpiece are in an effectivesanding position and press the abrasive in these pressure regions ontothe workpiece.

Furthermore, DE 27 57 314 and DE 1 921 566 disclose sanding machineshaving pneumatically operated pressure beams. The pneumatically operatedpressure beams are triggered by solenoid valves, so that the reactiontime is disadvantageously relatively long.

Disclosed in Austrian Patent AT 226105 is a non-oscillating belt sandingmachine in which a lamella-like pressure strip is moved at reduced speedparallel to an endless sanding belt. Due to the lamella-like surface ofthe pressure belt, which rests on the inside of the endless sanding beltand is pressed together with the latter onto the workpiece, the pressureon the sanding belt is not uniform over the sanding surface. On thecontrary, the pressure is exerted on the sanding belt in a continuouslyshifting manner and in a finely distributed manner at intervals over theentire length of the workpiece, so that the quality of the sanding andalso of the sanding performance can be substantially improved. In thiscase, the belt sanding machine is rigid and performs no oscillatingsanding movement.

SUMMARY OF THE INVENTION

The object of the invention is to provide an improved sanding machinewith which sanding marks can be reduced and a uniform sanding patterncan be ensured and in which sanding dust is optimally discharged.

This object is achieved with the sanding machine of the generic type inthat the activating device has a multiplicity of activating regionstriggered in such a way that various regions of the abrasive arealternately activated independently of the oscillating sanding movement.

According to the invention, therefore, an oscillating sanding movementknown from orbital sanders is combined with a rapidly changingactivation of selected sanding regions in such a way that theoscillating sanding movement is independent of the activation of thevarious regions of the abrasive. In contrast to conventional pressureshoes, however, the activating device according to the invention doesnot serve to assist the sanding of defined contours and prevent rotarysanding of workpiece edges. Rather, an image of the sanding marks isproduced by the alternate activation of various regions of the abrasive,this image thereby preventing an oscillating sanding movement fromproducing a regular sanding pattern. In addition, the alternateactivation of the various regions ensures that sanding dust can beoptimally discharged via the regions that are not activated.

The alternate activation is preferably effected in a rapidly changingmanner with regard to the relative feed rate between workpiece andsanding machine.

The activating regions are preferably triggered asynchronously relativeto the oscillating sanding movement, so that the grain of the sandingbelt is not in use continuously and the sanding patterns are obliteratedby the irregularly activated sanding regions.

The activating device can preferably be moved transversely to the feeddirection of the workpiece to be sanded. It is especially advantageousin this case if the activating regions of the activating device areraised lamellae on a carrier which is preferably designed as a platewhich can be moved in a reciprocating manner in the sanding planetransversely to the feed direction of the workpiece. Due to thereciprocating lamellae, which rest on the abrasive, the abrasive ispressed onto the workpiece only in the region of the lamellae. In thiscase, the reciprocating movement, running transversely to the feeddirection, of the plate is uncoupled from the feed movement and theoscillating sanding movement.

As an alternative to this, the lamellae may also be mounted on anendless conveying means, for example a chain conveyor, the endlessconveying means being driven in a revolving manner in the sanding planetransversely to the feed direction of the workpiece.

The revolving drive is again uncoupled from the oscillating sandingmovement and is preferably opposed to the oscillating sanding movementin the sanding plane.

The lamellae may extend relative to the sanding plane, for example,diagonally, in a V shape, in a W shape, in a curved manner or so as tobe offset one behind the other. These and other lamellae forms should beselected as a function of the construction of the sanding machine, ofthe type of oscillating sanding movement and of the sanding result.

Furthermore, it is advantageous if a pressure device known per se havingat least one pressure shoe which can be triggered is arranged betweenthe activating regions of the activating device and the abrasive. Incontrast to the activating device according to the invention, thispressure device serves to apply pressure to the abrasive as a functionof the contour of the workpiece, for example to prevent excessivesanding of marginal regions of the workpiece.

In an especially advantageous embodiment of the sanding machine, theabrasive, for example as a sanding sheet, is mounted on a retainingdevice. The retaining device is mounted with the oscillation drive meanson a sanding machine frame in such a way that the retaining device,relative to the sanding machine frame, is set in a sanding movementoscillating parallel to a sanding plane, i.e. the sanding surface of theabrasive. According to the invention, the activating device is coupledto the sanding machine frame and is uncoupled from the retaining deviceat least in one direction of the sanding plane. This ensures that thealternate activation of the various regions of the abrasive isindependent of the oscillating sanding movement.

In this case, the oscillation drive means preferably have rotatablydriven eccentric shafts which extend vertically to the sanding planebetween the sanding machine frame and the retaining device.

A rotating oscillating movement in the sanding plane is produced by theeccentricity of the driven shafts. At least one of the eccentric shaftsshould be displaceably mounted in one direction of the sanding plane inorder to reduce bearing loads which occur due to different linearexpansions during heating of the sanding machine. With a rigid bearingarrangement in the longitudinal direction of the eccentric shaft and inthe other directions of the sanding plane, a full oscillation stroke ofthe retaining device relative to the sanding machine frame is ensured.

In another embodiment, the activating device has flexible conduits forreceiving a medium and pressure control means which are connected to theconduits. The conduits provided may be tubes or chambers. The pressurecontrol means are provided in order to pressurize in a pulsating mannermedium located in the conduits, such as, for example, air or hydraulicfluid. In this way, pulsating waves of the medium are produced inconduit tubes, these waves exerting an increased pressure force on theabrasive adjoining the conduits in the region of the antinodes for theactivation. In the case of chambers as flexible conduits, the variouschambers can be triggered individually in order to apply pressurealternately to the various regions of the abrasive which adjoin thechambers.

The sanding machine may be designed as an orbital sander having asanding sheet which is interchangeably connected to the retainingdevice, for example in a clamping or adhering manner. However, theabrasive may also be a revolving endless sanding belt.

An especially uniform sanding pattern can be achieved if a plurality ofactivating devices of the type described above are arranged next to oneanother in the feed direction. The activating devices may bedisplaceably mounted on a common supporting beam. The supporting beam isthen moved in a reciprocating manner transversely to the feed direction,whereas the activating devices are in turn moved in a reciprocatingmanner relative to the supporting beam, for example in the longitudinaldirection of the supporting beam.

The object is also achieved by a method of sanding a workpiece using asanding machine described above by alternate activation of the abrasivein various regions of the abrasive, the activated regions beingtriggered independently of the oscillating sanding movement.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below with reference to theattached drawings. In the drawing:

FIG. 1 shows a perspective view of a first embodiment of a sandingmachine according to the invention;

FIG. 2 shows a perspective view of a detail of a sanding machine havinga retaining device for abrasive and an activating device;

FIG. 3 shows a perspective view of a second embodiment of a sandingmachine according to the invention having an endless sanding belt;

FIG. 4 shows a plan view of an activating device having an endlessconveying belt carrying lamellae;

FIG. 5 shows a cross-sectional side view of a detail of a thirdembodiment of a sanding machine according to the invention having twoactivating devices arranged next to one another in parallel;

FIG. 6 shows a cross-sectional side view of a detail of a sandingmachine having additional pressure devices;

FIG. 7 shows a front view of the sanding machine extending transverselyto the feed direction and having additional pressure devices from FIG.6.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 is a view transverse to the feed direction V, shows a sandingmachine according to the invention in cross section. An abrasive 1 inthe form of a sanding sheet or sanding belt is interchangeably attachedto a retaining device 2. The retaining device 2 is in turn carriedtransversely to the sanding plane, i.e. the sanding surface of theabrasive 1, by at least one eccentric shaft 3, which can be rotatablydriven at variable speeds by an electric motor 4. An orbital sandingmovement of the abrasive 1 in the sanding plane is produced by theeccentric shaft 3. The electric motor 4 is in turn firmly connected to asanding machine frame 5. The bearing arrangement of at least one of theeccentric shafts 3 provided should be displaceable in one direction ofthe sanding plane, preferably in the Y direction transversely to thefeed direction V, in order to compensate for linear expansions duringheating of the sanding machine and to reduce the bearing load. In thedirection in which the eccentric shaft 3 extends and also in the otherdirections of the sanding plane, the eccentric shaft 3 is preferablymounted rigidly and not flexibly in order to ensure the full oscillationstroke of the retaining device 2.

The abrasive 1 can be clamped, for example, onto the retaining device 2,can be tacked to the latter by a hook-and-loop connection or can bereleasably connected thereto in another way. The sanding machine maylikewise be designed with a sanding belt, drive rollers and/ordeflection devices for an endless sanding belt being coupled to theretaining device 2.

A workpiece 6 is guided along the sanding machine in feed direction Vrelative to the sanding belt 1. For the embodiment of a portable sandingmachine, this portable sanding machine may also be moved relative to afixed workpiece 6.

According to the invention, an activating device 7 having a multiplicityof activating regions 8, for example in the form of lamellae, which reston the abrasive 1 is provided between the retaining device 2 and theabrasive 1. The activating device 7 is moved independently of theoscillating sanding movement of the abrasive 1, for example in thesketched Y direction transversely to the feed direction V, and ispreferably directly coupled to the sanding machine frame 5. In thiscase, it is essential to the invention that the activating regions 8 ofthe activating device 7 are activated in such a way that various regionsof the abrasive 1 are alternately pressed onto the workpiece 6 by theactivating regions 8 independently of the oscillating sanding movement.The superimposed movements, not synchronized with one another, of theretaining device 2 (oscillating sanding movement) and the activatingdevice 7 (reciprocating movement) ensure that a regular sanding patternon account of the oscillating sanding movement is obliterated and theresulting sanding quality can thereby be considerably improved.

This result is essentially achieved by virtue of the fact that theactivating device 7 does not perform the oscillating movements of thesanding belt 1 but is largely uncoupled therefrom.

FIG. 2 shows a detail of the sanding machine from FIG. 1 as aperspective view.

It becomes clear that the abrasive 1 is interchangeably attached to aretaining plate 10 of the retaining device 2 by means of retaining rails9, for example in a clamping or adhering manner. In this case, theabrasive 1 is tensioned via activating regions 8 in the form ofdiagonally running lamellae of a plate-shaped carrier 11 of theactivating device 7. The plate-shaped carrier 11 of the activatingdevice 7 is moved in a reciprocating manner in the depicted Y arrowdirection transversely to the feed direction V by means of a motiondevice 12. In this case, the motion device 12 is preferably coupleddirectly to the sanding machine frame 5. The plate-shaped carrier 11 isguided laterally and vertically in guide elements 13 a, 13 b.

Whereas the abrasive 1 is set in a rotating oscillating sanding movementwith the retaining device 2, a reciprocating movement, independentthereof, of the activating device 7 is effected in the Y direction. Theplate-shaped carrier 11 is not affected by the oscillating sandingmovement and is mounted on the retaining device 2 in a freelydisplaceable manner in the sanding plane for this purpose.

The activating regions 8 may be raised diagonal lamellae as shown forexample, but may also be V-shaped, W-shaped or curved raised lamellae,raised lamellae arranged offset one behind the other or even irregularlyarranged raised lamellae. Further forms of the activating regions 8 areconceivable.

Essential is the resulting effect that only certain regions of theabrasive 1 are always pressed against the workpiece 6 by the activatingdevice 7 moved rapidly in a reciprocating manner, while the abrasive 1is set in a rapid sanding oscillation by the retaining device 2. Auniform pattern would be produced on the workpiece 6 by the oscillatingsanding movement. Owing to the fact that now only certain regions of theabrasive 1 are always activated, the otherwise uniform sanding marks areobliterated and better dust control is also obtained below the sandingbelt.

At least one further oscillating movement may be optionally superimposedon the simple oscillating movement of the retaining device 2.

FIG. 3 shows a perspective view of a sanding machine having a revolvingendless sanding belt 15 and an activating device 7 according to theinvention. Deflection and/or drive rollers 14 a, 14 b for the revolvingendless sanding belt 15 are carried by a retaining device 2 which is setin an oscillating sanding movement relative to the sanding machine frame5. To this end, at least one rotationally driven eccentric shaft 3 b isagain arranged between the sanding machine frame 5 and the retainingdevice 2.

The activating regions 8 of the activating device 7 rest on the innersurface of the endless sanding belt 15 in such a way that the sandingbelt 15 is pressed at the pressure regions 8 onto a workpiece (notshown) which is moved below the sanding belt 15 in feed direction Vrelative to the sanding machine.

FIG. 4 shows another embodiment of an activating device 7 in plan view.An endless conveying belt 16 is tensioned parallel to the sanding planetransversely to the feed direction V and carries a multiplicity ofspaced-apart activating regions 8 in the form of contact shoes. Thecontact surfaces of the contact shoes rest on the abrasive 1 in order topress the latter in the region of the contact shoes onto the workpiece 6to be sanded. The endless conveying belt 16 is, for example, an endlesschain deflected with sprocket wheels and driven in arrow direction P.

FIG. 5, in side view transversely to the feed direction V, shows adetail of a third embodiment of the sanding machine according to theinvention having two activating devices 7 a, 7 b arranged next to oneanother in parallel. The activating devices 7 a, 7 b each have amultiplicity of activating regions 8 a, 8 b, that extend transversely tothe feed direction V and are aligned with the sanding plane. Asupporting beam 17 is provided, which is either firmly mounted on thesanding machine frame 5 or is mounted on the retaining device 2 in sucha way as to be displaceable in at least one direction parallel to thesanding plane, so that the movement of the supporting beam 17 is largelyuncoupled from the oscillating sanding movement of the retaining device2.

Instead of a mechanical activating device, one or more flexible conduits18 or chambers may interact with the abrasive 1 as shown in FIG. 5. Themedium located in the conduits 18 or conduit chambers is pressurized ina pulsating manner by pressure control means, so that the regions of theabrasive 1 which are adjacent to the chambers to which pressure isapplied or the regions of the flexible conduits 18 in the region of theantinodes are pressed against the workpiece 6. By selection of the pulsecontrol or the activation of the individual chambers, the variousregions of the abrasive 1 can be pressed alternately against theworkpiece 6 independently of the oscillating sanding movement.

The activating regions 8 a, 8 b are rigidly mounted on the supportingbeam 17 in feed direction V by means of guide elements 19. Theactivating devices 7 a, 7 b may in turn again be mounted together withthe conduits 18 on the supporting beam 17 in such a, way as to bedisplaceable vertically to the sanding plane and may perform anadditional reciprocating movement.

The medium used may be, for example, air or hydraulic fluid.

FIG. 6 shows a detail of a fourth embodiment of the sanding machineaccording to the invention having two activating devices 7 a, 7 b whichare arranged next to one another in parallel and have an additionalpressure device known per se which has a multiplicity of pressure shoes20. By means of the pressure shoes 20, which can preferably be triggeredindividually, the respective activating regions 8 arranged thereon canbe displaced vertically to the sanding plane.

The pressure shoes 20 are fastened to a supporting beam 17, which inturn is mounted so as to be movable in a reciprocating mannertransversely to the feed direction V in order to activate the activatingregions 8 independently of the oscillating sanding movement.

FIG. 7 shows the sanding machine of the embodiment shown in FIG. 6 infront view. It becomes clear that the activating device 7 extendsparallel to the sanding plane transversely to the feed direction V, anda multiplicity of pressure shoes 20 of a pressure device known per seare provided spaced apart in the longitudinal direction of theactivating device 7. The pressure shoes 20 can be triggered, forexample, individually in order to specifically control the pressureforce in certain regions, in particular in order to prevent rotarysanding in marginal contours of the workpiece 6.

1. A sanding machine having oscillation drive means for setting anabrasive in an oscillating sanding movement, comprising an activatingdevice having a multiplicity of activating regions triggered in such away that various regions of the abrasive are alternately activatedindependently of the oscillating sanding movement, wherein the abrasiveis mounted on a retaining device and the retaining device is mountedwith the oscillation drive means on a sanding machine frame in order toset the retaining device, relative to a sanding machine frame, in asanding movement oscillating parallel to a sanding plane, which isdefined by a sanding surface of the abrasive, wherein the activatingdevice is coupled to the sanding machine frame and is uncoupled from theretaining device at least in one direction of the sanding plane, and theoscillation drive means have rotatably driven eccentric shafts whichextend vertically with respect to a sanding plane, between the sandingmachine frame and the retaining device, at least one of the eccentricshafts is displaceably mounted in one direction of a sanding plane. 2.The sanding machine as claimed in claim 1, wherein the activatingregions of the activating device are raised lamellae arranged on acarrier.
 3. The sanding machine as claimed in claim 1, wherein theactivating regions extend in a form of raised lamellae on a sandingplane diagonally, in a V shape, in a W shape, in a curved manner or soas to be offset one behind the other.
 4. The sanding machine as claimedin claim 1, further comprising a pressure device having at least onepressure shoe which can be triggered and is arranged between theactivating regions of the activating device and the abrasive.
 5. Thesanding machine as claimed in claim 1, further comprising, a pluralityof activating devices arranged one behind the other in the feeddirection.
 6. The sanding machine as claimed in claim 1, wherein theabrasive is a sanding sheet interchangeably connected to the retainingdevice.
 7. The sanding machine as claimed in claim 1, wherein theactivating device has flexible conduits for receiving a medium, andpressure control means are connected to the conduits, medium located inthe conduits being pressurized in a pulsating manner by the pressurecontrol means.
 8. The sanding machine as claimed in claim 1, wherein theabrasive is a revolving endless sanding belt.